1. Field of the invention
The invention relates to a method and an installation or apparatus for the treatment of material contaminated with toxic organic compounds in which the material is heated in a rotary furnace to thermally destroy or decompose the toxic compounds and in which the gaseous reaction products are separated from the solid reaction products and burnt in a combustion chamber.
2. Description of the prior art
In many industrial countries, but also in so called developing countries, there are larger and smaller areas or terrain contaminated or polluted with highly toxic organic substances. The most dangerous of these highly toxic organic compounds are those of the group comprising polychlorobiphenylenes (PCBs, dioxins, including tetrachlorodibenzodioxin (TCDD), furans and polycyclic aromatic hydrocarbons (PAHs). In some cases it was not until recent years that the danger of these substances for the health of humans was established.
Previously, however, in many cases for decades in the chemical industry waste materials were produced containing these highly toxic substances. These waste materials were usually stored in liquid or solid form in dumps or in wastewater ponds or sludge tank,, where in most cases they still are today. There are other relatively large areas in which the entire topsoil is contaminated by gas and dust emissions which were polluted with the highly toxic substances.
For ecological and health reasons it is therefore urgently necessary to detoxicate the contaminated areas by corresponding treatment of the entire toxicated earth and rock, contaminated waters and waste water and polluted rubbish and muds. Since enormous quantities of contaminated material are involved, a decisive factor in the implementation of corresponding recultivation programs is that the methods and installations used involve acceptable technical and economic expenditure, which means that they can be carried out with the minimum energy consumption and have at the same time a high efficiency.
Because of the extremely high toxicity of the substances and compounds mention the remainder of toxic substances inevitably remaining in the treated materials should not exceed the concentration of a few ppb (parts per billion). Only when this limit value has been reached or bettered can the contaminated material be reused or utilized.
A known method for the treating of material contaminated with toxic organic compounds which is however still in the experimental stage is the extraction method. In this method an attempt is made either with the aid of organic solvents, of steam or organic solvents and steam together to extract the toxic substance from the contaminated materials and then separate them from the extracts for example by evaporating the solvent or water. This method has however many disadvantages: the efficiency of the method is too low to enable the required limit value in the ppb range to be reached; the organic solvents necessary for the extraction are usually themselves toxic and it is forbidden by law for them to be introduced into the earth, water or air: the organic solvents must be driven out of the soil treated therewith again by a thermal treatment, condensed in a corresponding apparatus and this recovered, and this requires a high consumption of energy.
Another known method for the treatment of material contaminated with toxic organic compounds is burning. In this method the contaminated material is heated in a furnace, usually a directly heated rotary furnace, to a temperature far above 1000.degree. C. and the flue gas thereby generated thermally cracked at a still higher temperature of about 1200.degree. C. and with a residence time of at least 2 seconds to completely destroy the thermally very stable toxic compounds.
This known method also has serious disadvantages: The heating of large amounts of materials to temperatures of 1000.degree. to 1200 .degree. C. requires an enormous amount of fuel, not only because of the high temperatures on their own but also because the burning of such stable compounds requires a great deal of oxygen so that large quantities of air must be transported into the combustion chamber and heated. Inevitably a high ballast component is thereby entrained which must also be heated to these high temperatures, i.e. the nitrogen of the air which does not participate in the combustion operation. The specific energy requirement with this method is thus extremely high, making the overall method uneconomical. A further disadvantage of the known burning method is that the materials which are usually moist on introduction into the combustion furnace because of the intense thermal radiation in the furnace very rapidly become incrusted on the surface. The incrustation makes the surface of the materials increasingly dense and thus increasingly impermeable to gases which are to be driven out of the interior of the material and into the furnace atmosphere and withdrawn from the latter. Consequently, the incrustation of the material prevents an effective detoxication.
One object of this invention is therefore to provide a method for the treatment of material contaminated with toxic organic compounds which is more economical than the hitherto known methods, has a lower energy requirement and a higher efficiency.
Another object of this invention is to provide a method with which it is possible to reduce the concentration of toxic organic compounds in the material treated to the ppb range, preferably to 1 ppb or below.
A further object of this invention is to provide an installation or apparatus for the treatment of material contaminated with toxic organic compounds with which the method according to the invention can be carried out in simple and economical but at the same time effective manner.
A still further object of this invention is finally to provide an installation for the treatment of material contaminated with toxic organic compounds which is mobile and in the case of an accident or catastrophe can rapidly be brought to the place of use.
Still further objects of this invention may be seen from the description in this specification and the attached drawing.